PROCEEDINGS OF THE rOLYTECHNIC ASSOCIATION. 815 



of these relations, that of attraction, obtains in the solid condition 

 of matter; in the liquid state, the atoms approximate to the second 

 relation or that of equilibrinm; and in the Jluid or gaseous state to 

 the third or that of repulsion. 



In the gaseous condition the atoms move with great velocity in 

 straight lines, or verj' flat hyperbolas, and the virtual or resultant 

 repulsion causes them constantly to tend to diffuse themselves 

 through a greater space, which tendency is only limited by the 

 exercise of a powerful external gravitation towards some heavy 

 object like the earth, or the coercive power of containing surfaces 

 of solid or liquid bodies. 



The supposed etherial medium of the celestial spaces, if it exists, 

 may be composed of atoms whose almost infinitcssimal amount of 

 inertia, when compared with atoms of grosser matter, is compeA- 

 sated to some extent by their enormous velocity of motion. 



The equilibrium of the liquid state would, according to this 

 view, be an unstable one, and there should, apparently, be no 

 interval between the temperatures of congelation or liqueftiction 

 and that of ebullition. There are, however, important modifying 

 circumstances, to be hereafter considered, connected with these 

 transformations, among which are the restraining influence of 

 external "pressure" and the evolution and absorption of "latent 

 heat," which occasion an interval of variable width, in different 

 substances, between the temperatures at which the two transform- 

 ations occur. 



Yet, in every part of this interval, liquids have a tendency to 

 assume the gaseous form or to emporate, this tendency depending 

 in part on the amount of similar vapor already contained in the 

 surrounding space or medium, and in part on the extei'nal pressure 

 and temperature. So that if to the surface of a liquid, a vacuum 

 or unsaturated medium is continually presented, the liquid will 

 gradually and entirely evaporate at any temperature above its 

 congealing point. Although this evaporation goes on with extreme 

 slowness among certain substances like fixed oils, etc., the unsti.ble 

 nature of the liquid condition is more or less evident in all knoAvn 

 liquids. 



In the investigation of the changes which take place in the 

 atomic orbits during these transformations we have to consider the 

 motions, not alone of single pairs but of vast numbers of aggre- 

 gated atoms, a fact which adds immensely to the complication and 



